1) Field of the Invention
The present invention relates to a belt-type continuously variable transmission control device having an actuator on each of a primary pulley and a secondary pulley for generating a belt pinching pressures.
2) Description of the Related Art
Generally, a belt-type continuously variable transmission (CVT) includes two rotary shafts arranged in parallel, a primary pulley and a secondary pulley attached to the respective shafts, and a belt wound on V grooves of each of the primary pulley and the secondary pulley. Each of the primary pulley and the secondary pulley includes a fixed sheave, which is conical and fixed to the corresponding rotary shaft, and a movable sheave, which is also conical but slides on the rotary shaft in an axial direction. The V groove is formed by inclined parts of the fixed sheave and the movable sheave that are opposed to each other.
The belt-type CVT of this type causes the contact radii of the belt in contact with the primary pulley and the secondary pulley to continuously change. Moreover, a gear ratio γ is continuously changed by sliding the movable sheave on the rotary shaft and by changing a width of the V groove of the pulley. The gear ratio γ is a ratio of the contact radius of the belt in contact with the primary pulley to that of the belt in contact with the secondary pulley. In other words, it is possible to continuously and variably change the gear ratio γ by controlling the groove width of only the primary pulley.
Thus, it is necessary to slide the movable sheave on the rotary shaft to change the gear ratio γ. Therefore, a mechanism (a movable sheave sliding mechanism) that slides the movable sheave of the primary pulley becomes necessary. An exemplary movable sheave sliding mechanism slides the movable sheave with a motor such as an electric motor or a hydraulic motor.
This belt-type CVT is also equipped with a pressure mechanism (an actuator) that presses the movable sheave against the fixed sheave and that generates a belt pinching pressure so as to keep the gear ratio γ and to prevent slippage of the belt on the pulleys. An exemplary pressure mechanism generates the belt pinching pressure by oil pressure or air pressure within a cylinder provided on a rear surface of the movable sheave (a surface thereof opposite to the V groove). Another exemplary pressure mechanism generates the belt pinching pressure by a torque cam provided on the rear surface of the movable sheave. A belt-type CVT with a pressure mechanism is disclosed in, for example, Japanese Utility Model Application Laid-Open No. S64-12960.
The pressure mechanism generates the belt pinching pressure by appropriately changing the oil pressure depending on a torque input to the belt-type CVT.
The torque input to the belt-type CVT can be the torque of an internal combustion engine that is stored in advance corresponding to the driving conditions. However, the problem is that the torque stored is not always same as the actual torque output from the internal combustion engine. This is due to the fluctuations in the characteristics of the internal combustion engine. If the torque stored is same as the actual torque, the belt pinching-pressure generated is in error, that is, the belt pinching pressure cannot be controlled appropriately.
It is an object of the preset invention to provide a belt-type continuously variable transmission control device that can input an accurate torque to a pressure mechanism of the belt-type CVT.